Unix: A History and a Memoir by Kernighan is really good.
There's a lot of fun historical information and anecdotes. But, since our modern systems still have a lot of Unix ideas at their roots, I also came away with a better understanding of how to use today's systems.
This book provided me a real appreciation for the innovative concepts the original UNIX developers came up with so many years ago. Their impact cannot be overstated.
Highly recommended read for anyone who happens to spend their time plotting away in a terminal.
There's a lot of fun historical information and anecdotes. But, since our modern systems still have a lot of Unix ideas at their roots, I also came away with a better understanding of how to use today's systems.